diff options
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 8 | ||||
| -rw-r--r-- | kernel/rcu/tasks.h | 27 |
2 files changed, 31 insertions, 4 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9b09fc5dfe66..089f4c5f8225 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4805,6 +4805,14 @@ period to instead use normal non-expedited grace-period processing. + rcupdate.rcu_task_contend_lim= [KNL] + Set the minimum number of callback-queuing-time + lock-contention events per jiffy required to + cause the RCU Tasks flavors to switch to per-CPU + callback queuing. This switching only occurs + when rcupdate.rcu_task_enqueue_lim is set to + the default value of -1. + rcupdate.rcu_task_enqueue_lim= [KNL] Set the number of callback queues to use for the RCU Tasks family of RCU flavors. The default diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 6e8e4cf6fff3..d37ab69b9db8 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -142,6 +142,10 @@ module_param(rcu_task_stall_timeout, int, 0644); static int rcu_task_enqueue_lim __read_mostly = -1; module_param(rcu_task_enqueue_lim, int, 0444); +static bool rcu_task_cb_adjust; +static int rcu_task_contend_lim __read_mostly = 100; +module_param(rcu_task_contend_lim, int, 0444); + /* RCU tasks grace-period state for debugging. */ #define RTGS_INIT 0 #define RTGS_WAIT_WAIT_CBS 1 @@ -207,10 +211,13 @@ static void cblist_init_generic(struct rcu_tasks *rtp) int lim; raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); - if (rcu_task_enqueue_lim < 0) - rcu_task_enqueue_lim = nr_cpu_ids; - else if (rcu_task_enqueue_lim == 0) + if (rcu_task_enqueue_lim < 0) { + rcu_task_enqueue_lim = 1; + rcu_task_cb_adjust = true; + pr_info("%s: Setting adjustable number of callback queues.\n", __func__); + } else if (rcu_task_enqueue_lim == 0) { rcu_task_enqueue_lim = 1; + } lim = rcu_task_enqueue_lim; if (lim > nr_cpu_ids) @@ -251,6 +258,7 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, { unsigned long flags; unsigned long j; + bool needadjust = false; bool needwake; struct rcu_tasks_percpu *rtpcp; @@ -266,7 +274,9 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, rtpcp->rtp_jiffies = j; rtpcp->rtp_n_lock_retries = 0; } - rtpcp->rtp_n_lock_retries++; + if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim && + READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids) + needadjust = true; // Defer adjustment to avoid deadlock. } if (!rcu_segcblist_is_enabled(&rtpcp->cblist)) { raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled. @@ -276,6 +286,15 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, needwake = rcu_segcblist_empty(&rtpcp->cblist); rcu_segcblist_enqueue(&rtpcp->cblist, rhp); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + if (unlikely(needadjust)) { + raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); + if (rtp->percpu_enqueue_lim != nr_cpu_ids) { + WRITE_ONCE(rtp->percpu_enqueue_shift, ilog2(nr_cpu_ids)); + smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids); + pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name); + } + raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); + } /* We can't create the thread unless interrupts are enabled. */ if (needwake && READ_ONCE(rtp->kthread_ptr)) irq_work_queue(&rtpcp->rtp_irq_work); |